I'd love to see an app that allows iOS and Android users to exchange BTC by bumping phones. The app would still be able to manually send to addresses and scan QR codes, but the bumping would be the primary method of exchanging addresses and transferring coins. It would use the bu.mp API.
I think an app like this would be great for Bitcoin's adoption.
I'd offer maybe 2 or 3 BTC. I don't know about the amount.
I think the problem with iOS (as usual) is that Apple won't allow Bitcoin related apps into the app store. At least that's what I read some times. (And the control it exercises over its closed walled garden ecosystem is the reason why I would never, never, ever buy a product of theirs.)